This invention relates to apparatus for cleaning and drying a surface and, in particular, apparatus for cleaning and drying the photoconductive imaging surface of a liquid developer electrophotographic copier.
Electrophotographic copiers of the image transfer type, or plain paper copiers, as they are generally known, are well-known in the art. In one type of image transfer copier the electrostatic image formed by selectively discharging a photoconductive surface is subjected to the action of a liquid developer to form a visible image corresponding to the latent image. The developed image thus formed is then transferred to a sheet of plain paper and the photoconductive surface is then available to be used for a subsequent copying operation. Owing to the fact that the transfer of the developed image between the photoconductive surface and the sheet of plain paper is incomplete, a residual image remains on the photoconductive surface which must be cleaned before being reused. In copiers of the type which employ liquid developers it is not only necessary that the toner particles remaining after transfer be removed but also the surface of the drum should be wiped as dry as possible prior to the next copying operation. Cleaning arrangements heretofore employed in liquid developer electrostatic copiers typically employ a two-step operation in which the photoconductive surface is first moved past a wetted spongy roller formed of open-cell material to scrub residual toner particles from the surface and is then moved past an elongated squeegee blade to wipe the surface dry. While this and similar arrangements satisfactorily clean the photoconductive surface, the two-step nature of the cleaning and drying operation introduces an undesirable complexity into the design of the system. Further, the abrasion of the photoconductive surface due to the action of the roller and blade typically used, while initially small, is nevertheless appreciable and over a long period of time will degrade the image reproducing capability of the photoconductive surface. The open-cell foam roller tends to soak up cleaning liquid, resulting in objectionable fumes as the liquid evaporates. In addition, buildup of toner particles on the roller and blade as time passes increase the abrasive action of these elements on the photoconductive surface.
U.S. Pat. No. 3,807,853, issued to F. W. Hudson, discloses a cleaning apparatus for a dry developer electrophotographic copier in which a roller formed from open-cell or closed-cell material which preferably is polyurethane is driven in frictional engagement with the photoconductive surface sufficient impact to sweep remaining dry developer toner particles therefrom. The roller surface then moves past a doctor blade which abrades against the roller surface with sufficient force to enter the cellular structure and scrape the toner particles therefrom.
While the patentee speaks in passing near the end of the specification of using the roller in conjunction with marking materials such as "inks", it is abundantly clear from the disclosure that the patentee contemplates only removal of dry particles from the surface of the photoconductor. To this end to remove the dry trapped toner particles from the roller cells, the patentee orients the scraper blade with its knife edge digging sharply into the roller surface against the direction of motion thereof so that the blade in effect scoops the particles out of the cells by entering the same. This orientation of the scraper blade, while necessary for removal of dry powder from the roll cells obviously, is highly abrasive and results in a very short useful life of the roller. This problem is aggravated by the fact that the patentee prefers a roller formed of relatively soft and nonabrading material so as not to damage the imaging surface itself.
Even with this highly abrasive method of removing the trapped toner particles from the surface cells of the roller, the purely mechanical method contemplated cannot ensure complete evacuation of the surface cells. As a result, the roller will sweep residual toner particles past the imaging surface on subsequent rotation, damaging the imaging surface over a long period of time.
Finally, if the roller of open-cell material described by the patentee as one of the two equivalent materials were to be used in a liquid developer copier, either the surface would not be dry in the absence of a wiper blade or, if a wiper blade is used, the system would involve the same defects as do systems of the prior art. Moreover, if the open-cell roller and scraper blade of Hudson were used in a liquid developer machine the scraper blade would be ineffective to remove either toner liquid or trapped toner particles from the interior cells of the roller and would thus not avoid the previously noted problems of clogging or fume emission.